Solid-to-Hybrid Transitioning Armature Railgun With Non-Conforming-To-Prejudice Bore Profile

ABSTRACT

An improved railgun, railgun barrel, railgun projectile, and railgun system for accelerating a solid-to-hybrid transitioning armature projectile using a barrel having a bore that does not conform to a cross-sectional profile of the projectile, to contact and guide the projectile only by the rails in a low pressure bore volume so as to minimize damage, failure, and/or underperformance caused by plasma armatures, insulator ablation, and/or restrikes.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/345,920, filed May 18, 2010 and incorporated by reference herein.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The United States Government has rights in this invention pursuant toContract No. DE-AC52-07NA27344 between the United States Department ofEnergy and Lawrence Livermore National Security, LLC for the operationof Lawrence Livermore National Laboratory.

FIELD OF THE INVENTION

The present invention relates to railguns. More particularly, theinvention relates to an improved railgun, railgun barrel, railgunprojectile, and railgun system for accelerating a solid-to-hybridtransitioning armature projectile using a barrel having a barrel borethat does not conform to a cross-sectional profile of the projectile, tocontact and guide the projectile only by the rails in a low pressurebore volume so as to minimize damage, failure, and/or underperformancecaused by plasma armatures, insulator ablation, and/or restrikes.

BACKGROUND OF THE INVENTION

Railguns are electrical guns known to accelerate projectiles along apair of electrically conductive rails by permitting a large electriccurrent to pass between the pair of rails by way of a conductive mediumof, produced by, or otherwise associated with the projectile. Thiscurrent interacts with the strong magnetic fields generated by the railsto accelerate the projectile using the same principles as the homopolarmotor, and have been known to achieve velocities greater than what istypically achievable by conventional firearms-based technology. Forexample, railguns have been used in experiments to accelerate gram-sizedand larger objects to speeds of 6 km/sec.

Various approaches are known for accelerating projectiles usingrailguns. One approach relies on a column of electrically conductive gasto produce a plasma armature to provide the propulsive force, in theform of gas pressure, to a non-conductive sabot typically made of ahigh-strength plastic, such as for example Lexan. It is appreciated thata plasma armature involves rail-to-rail plasma arcing. Other operatingmodes involve (1) using a solid conductor in contact with the rails forproducing a solid armature, (2) using a transitioning hybrid armaturewhich operates with both plasma arcing as well as conduction through asolid (plasma-solid-plasma conduction), and (3) tandem operation, whichcan involve both plasma armature and hybrid armature operation. It isnotable, however, that plasma armatures have deleterious effects onrailgun operation and projectile velocities, due to for example ablationdrag, restrike, etc. Therefore plasma

One example railgun is shown in the article “The Gas-Insulated-Railgun”by Tidman, Parker, et. al., which uses a high-pressure gas fill in asteel tube. In this configuration a trailing wake can be produced, andat the wake boundary there is likely to be a region exactly at the“Paschen minimum”, i.e. where the value of pressure for the rail-to-railgap at which the breakdown voltage is a minimum. This situation islikely to produce restrike arcs in the wake.

Another example is shown in the article “Railgun Performance with aTwo-Stage Light-Gas Gun Injector” by Hawke, Suseoff, et. al., whichinvolves a projectile-conforming sealed barrel design, along with asolid/hybrid transitioning armature. Because of the conforming barrelbore (i.e. barrel walls substantially conform to the cross-sectionalprofile of the projectile), it is typical in such designs that a plasmaarmature forms behind the hybrid armature (i.e. referred to as “tandem”operation). This is likely because the plasma cannot be completelycontained within the hybrid and leaks rearward. The conforming barrelbore provides a means to support a non-zero plasma pressure and hence anon-zero plasma conductivity; the hot plasma in the rear of the armatureproviding a conductive path which inevitably leads to a plasma armaturein the rear. In fact the experimental results show that tandem operationcommences almost immediately. However, once a plasma armature forms inthe back, all the deleterious effects of a plasma armature arise, i.e.ablation drag, restrike, etc.

And another example is described in the article “A Transitioning HybridArmature Concept” by Trevor James, which involves hybrid armature in aprojectile conforming barrel bore, where the “plasma brushes” live inthe “legs” of an otherwise “C-shaped” solid armature. The conceptattempts to control the plasma armature pressure usingradially-inward-directed “exhaust ducts”. This design is likely tooperate in the “tandem” mode (hybrid armature plus plasma armature) atultra-high-velocities, since the hot, conductive exhaust gases aredirected rearward in a closed barrel, leading to tandem operation in asimilar manner as in the Hawke, Suseoff article. For Ultra-High-Velocityoperation tandem operation is not desirable for same reasons asdiscussed for the Hawke, Suseoff design.

As such, there is a need for a railgun designed to operate without andprevent the formation of plasma armatures, to enable high and ultra-highvelocities in railgun applications.

SUMMARY OF THE INVENTION

One aspect of the present invention includes a railgun comprising: abarrel having a pair of parallel conductive rails each with a convexrail surface facing the other convex rail surface with only said convexrail surfaces of the rails adapted to contact (“rail-only contact”) aprojectile launched through the barrel; a barrel bore defined betweenand in part by said convex rail surfaces and having a cross-sectionalprofile (“non-conforming-to-projectile bore profile”) that does notcompletely conform to a cross-sectional profile of the projectile; andan enclosure surrounding the barrel bore and filled with a low-pressuregas, whereby the rail-only contact, the non-conforming-to-projectilebore profile, and the low-pressure gas in the enclosure contribute tominimizing plasma armature formation and restrikes.

Another aspect of the present invention includes a railgun projectilecomprising, a nonconductive sabot; and a conductive section connected tothe sabot and having a rear conductive section with a pair of contactsurfaces each for contacting a corresponding one of the convex railsurfaces and a forward conductive section spanning less than a gapdistance between the convex rail surfaces, wherein the rear section andthe forward section are adapted so that when the projectile isaccelerated along an energized pair of parallel conducting rails, in afirst stage of acceleration an electrical current is produced across therear conductive section as a solid armature to accelerate the projectileuntil the rear conductive section is ablated prior to reaching themuzzle end of the barrel, and in a second stage of acceleration anelectrical current is produced across the forward section as a hybridarmature to accelerate the projectile out through the muzzle end of thebarrel.

Another aspect of the present invention includes a railgun systemcomprising: a barrel having a breech end, a muzzle end, a pair ofparallel conductive rails extending between the breech and muzzle ends,with each conductive rail having a convex rail surface facing the otherconvex rail surface with only said convex rail surfaces of the railsadapted to contact (“rail-only contact”) a projectile launched throughthe barrel; a barrel bore defined between and in part by said convexrail surfaces and having a cross-sectional profile(“non-conforming-to-projectile bore profile”) that does not completelyconform to a cross-sectional profile of the projectile; and an enclosuresurrounding the barrel bore and filled with a low-pressure gas, wherebythe rail-only contact, the non-conforming-to-projectile bore profile,and the low-pressure gas in the enclosure contribute to minimizingplasma armature formation and restrikes; and a projectile having anonconductive sabot, and a conductive section connected to the sabot andhaving a rear conductive section with a pair of contact surfaces eachfor contacting a corresponding one of the convex rail surfaces, and aforward conductive section spanning less than a gap distance between theconvex rail surfaces, wherein the rear section and the forward sectionare adapted so that upon connecting the conductive rails to a voltagesource, in a first stage of acceleration an electrical current isproduced across the rear conductive section as a solid armature toaccelerate the projectile until the rear conductive section is ablatedprior to reaching the muzzle end of the barrel, and in a second stage ofacceleration an electrical current is produced across the forwardsection as a hybrid armature to accelerate the projectile out throughthe muzzle end of the barrel.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the disclosure, are as follows.

FIG. 1A is a cross-sectional view of a first exemplary embodiment of theopen barrel (i.e. having non-conforming-to-projectile barrel bore) ofthe present invention.

FIG. 1B is a cross-sectional view of a first exemplary embodiment of theopen barrel (i.e. having non-conforming-to-projectile barrel bore) ofthe present invention also shown with a layer of energy-absorbingsubstance on the dielectric surfaces.

FIG. 1 is a cross-sectional view of a first exemplary embodiment of theopen barrel (i.e. having non-conforming-to-projectile barrel bore) ofthe present invention.

FIG. 2A is a cross-sectional view of the exemplary embodiment of FIG.2B.

FIG. 2B is a top view of a section of the barrel of the presentinvention, including an exemplary embodiment of the projectile of thepresent invention.

FIG. 3A-C show side, top and back end views, respectively of theconductive section of the projectile.

FIGS. 4A-B show time lapsed views of an exemplary projectile embodimentas it is launched in the barrel of the present invention.

FIG. 5A shows another embodiment of the projectile having a frontpayload.

FIG. 5B shows another embodiment of the projectile having a rearpayload.

FIG. 6 is a cross-sectional view of another exemplary embodiment of theopen barrel shown with ports for introducing a low pressure gas.

FIG. 7 is a cross-sectional view of another exemplary embodiment of theopen barrel including augementing rails.

FIG. 8 is a schematic view of another embodiment of the presentinvention shown a barrel configuration with segmented primary rails, aninjector, and augmenting rails.

DETAILED DESCRIPTION

Generally, the present invention is a railgun designed to launch aprojectile to high velocities and ultra-high velocities (e.g. greaterthan 6 km/sec, such as 10-15 km/sec) using an “open barrel” architecture(e.g. rail-only contact with projectile and anon-conforming-to-projectile bore profile), a solid-to-hybridtransitioning armature, and low pressure gas fill to increaserail-to-rail breakdown voltage, which together contribute to minimizeand avoid the deleterious effects associated with plasma armatureformation and tandem operation, which may include restrikes.

Turning now to the drawings, FIG. 1A shows a first exemplary embodimentof the open barrel structure of the present invention. In particular,FIG. 1A shows a barrel 100 having a pair of parallel conductive rails 12defining in part a barrel bore 16 therebetween (which is shown occupiedin part by projectile 10). The rails 12 are shown having convective railsurfaces 12′ facing each other across the barrel bore 16. Furthermore,only the convex rail surfaces of the rails are adapted to contact theprojectile 10 that is launched through the barrel, and is characterizedas “rail-only contact”. FIG. 1A also shows a projectile 10 positioned inthe barrel bore 16 between the rails 12. which mate with concave surfaceof the projectile. The open space above and below the projectile is animportant feature for mitigating plasma armature formation and secondardstrikes (restrikes). As shown in FIG. 1A, it is notable that only theconvex rail surfaces come in contact with the projectile. No other partsof the barrel, including the dielectric wall surfaces come in contactwith the projectile.

In this embodiment, dielectric walls 14 are also shown provided andforming an enclosure, which also define in part the barrel bore,together with the convex rail surfaces. The pair of dielectric sidewalls14 each have a dielectric sidewall surface 14′ facing the otherdielectric sidewall surface 14′, and which are positioned away from theprojectile 10 so that the barrel bore 16 is characterized as notcompletely conforming to the cross-sectional profile of the projectile(“non-conforming-to-projectile bore profile”). In fact, it can be seenthat the area covered by the cross-sectional bore profile is larger thanthe cross-sectional profile of the projectile 10. While it isappreciated that some conforming to the projectile profile inherentlyexists dues to the mating surfaces between the projectile and the convexrail surfaces, it is not completely conforming since no other barrelsurface is positioned adjacent the projectile.

Generally, the open barrel configuration of the present invention has a“non-conforming-to-projectile” barrel bore, which, as used herein in theclaims, is a type surrounded and defined by a barrel wall or walls whichdo not substantially conform to the diametric or cross-sectional profileof the projectile, and thus subjects the projectile to contact on only alimited number (less than all) of its sides by the barrel wall(s) forguiding the projectile as it travels through the barrel. In the presentinvention, the barrel wall sections which do come in contact with theprojectile are a pair of conductive rails (rail-only contact) which alsosupply the electromotive force which launches the projectile through thebarrel. All other projectile surfaces not in contact with or adjacentthe conductive rails are adjacent an open space, which may be theexterior environment in the case of a rail-only, partially wall-lessdesign, or the hollow space inside an enclosed barrel chamber. Incontrast, a projectile conforming barrel bore is a bore whichsubstantially conforms to the diametric or cross-sectional profile ofthe projectile. In particular, the barrel wall or walls of the barrelsubstantially conform to the diametric or cross-sectional profile of theprojectile, as exemplified by the gun barrels of most conventionalfirearms, and thus subjects the projectile to contact on all sides (withthe exception of the front and rear) by the barrel walls for guiding theprojectile as it travels through the barrel.

The present invention also relies on a low-pressure (e.g. all the waydown to a perfect vacuum) gas fill, with the ambient pressure below thePaschen minimum, and hence restrike in the wake is averted. Inparticular, the enclosure 14 in FIG. 1A surrounding the barrel bore isfilled with a low-pressure gas. The reason for a “low pressure” gas fillis that certain gases such as SF6 have a greater minimum breakdownvoltage than air, and hence a prefill of this gas (followed by a pumpingdown to a low pressure) is desirable for increased performance.“Low-pressure” may include, for example, 2 atm or less pressure. Inparticular, the low-pressure gas is of a type capable of increasingrail-to-rail breakdown voltage in the presence of high temperature metalvapor. The gas is preferably supplied via ports 36 shown in FIG. 6showing embodiment 600. The open barrel architecture and low-pressuregas help eliminate plasma armature or tandem operation, since withoutsidewalls closely positioned adjacent the projectile the gas in the tailcannot maintain a non-zero pressure, and hence cannot sustain aconductive path.

And FIG. 1B shows a second exemplary embodiment of the open-barrelstructure of the present invention. In particular, FIG. 1B shows thedielectric surfaces coated with an energy-absorbing material 18, asknown in the art, capable of vaporizing to a low-temperature dielectricgas, which also prevents and minimizes restrikes.

FIGS. 2A-2B show an exemplary projectile 10 positioned in the barrelbore of the present invention. In particular, the projectile 10 has anonconductive sabot 20 (may include payload) at a leading end, and aconductive section connected to the sabot. The conductive sectionincludes a rear conductive section 11′ shown as a pair of C-shaped“wings” 24 with a pair of contact surfaces, each contact surface forcontacting a corresponding one of the convex rail surfaces of theconductive rails 12, and a forward conductive section 11 spanning lessthan a gap distance between the convex rail surfaces. Additional viewsof the projectile and its two sections are shown in FIGS. 3A-C.

And FIGS. 4A and 4B show the transition from solid armatures (FIG. 4A)to a hybrid armature (FIG. 4B) of the conductive section of theprojectile as it is launched in the direction 30. A sabot is shown aheadof the conductive section, and plasma arcing is shown at 28 in FIG. 4B.In particular, the rear section and the forward section are adapted sothat upon connecting the conductive rails to a voltage source, in afirst stage of acceleration (shown in FIG. 4A), an electrical current isproduced across the rear conductive section as a solid armature toaccelerate the projectile. In particular, the rear conductive section isconfigured to be ablated prior to reaching the muzzle end of the barrel.And in a second stage of acceleration an electrical current is producedacross the forward section as a hybrid armature to accelerate theprojectile out through the muzzle end of the barrel. The rear section ispreferably made of a material with a melting point less than apredetermined operating temperature of the railgun so as to melt awayand reduce parasitic mass as the armature accelerates along the rails.

And FIGS. 5A and 5B show two exemplary embodiments 500 and 501 of theprojectiles showing a sabot 32 with payloads in front and to the rear ofthe conductive section. In particular, FIG. 5B shows a tail or shroud 34which extends to the rear of the conductive section.

FIG. 7 show another embodiment 700 showing the use of augmenting rails38 which augment the primary rails by decreasing the required armaturecurrent for a given acceleration, and/or increase the stagnationvelocity of free-running precursor or secondary arcs. At least oneadditional pair of parallel conductive rails (“augmenting rails”) may bepositioned adjacent the first pair of parallel conductive rails. FIG. 8also shows the use of augmenting railsprimary rails in embodiment 800.FIG. 8 also shows the segmentation of the primary rails into multiplesections 40 and 41, where a current 42 a is provided for segment 40while a different current 42 b is provided for segment 41. The pair ofconductive rails are segmented along the length of the barrel with eachrail segment powered independently from other segments. Projectilepre-acceleration is also shown in FIG. 8 using an injector 48 forinjecting the projectile at the breech end of the barrel.

While particular embodiments and parameters have been described and/orillustrated, such are not intended to be limiting. Modifications andchanges may become apparent to those skilled in the art, and it isintended that the invention be limited only by the scope of the appendedclaims.

1. A railgun comprising: a barrel having a pair of parallel conductiverails each with a convex rail surface facing the other convex railsurface with only said convex rail surfaces of the rails adapted tocontact (“rail-only contact”) a projectile launched through the barrel;a barrel bore defined between and in part by said convex rail surfacesand having a cross-sectional profile (“non-conforming-to-projectile boreprofile”) that does not completely conform to a cross-sectional profileof the projectile; and an enclosure surrounding the barrel bore andfilled with a low-pressure gas, whereby the rail-only contact, thenon-conforming-to-projectile bore profile, and the low-pressure gas inthe enclosure contribute to minimizing plasma armature formation andrestrikes.
 2. The railgun of claim 1, wherein the barrel furtherincludes a pair of dielectric sidewalls each having a dielectricsidewall surface facing the other dielectric sidewall surface, with thedielectric sidewall surfaces defining in part the barrel bore andpositioned so as not to contact the projectile.
 3. The railgun of claim2, wherein the dielectric sidewall surfaces have an energy absorbingmaterial thereon capable of vaporizing to a low-temperature dielectricgas.
 4. The railgun of claim 1, wherein the pair of conductive rails aresegmented along the length of the barrel with each rail segment poweredindependently from other segments.
 5. The railgun of claim 1, furthercomprising at least one additional pair of parallel conductive rails(“augmenting rails”) positioned adjacent the first pair of parallelconductive rails.
 6. The railgun of claim 1, further comprising aninjector connected to pre-accelerate the projectile into a breech end ofthe barrel.
 7. A railgun projectile comprising, a nonconductive sabot;and a conductive section connected to the sabot and having a rearconductive section with a pair of contact surfaces each for contacting acorresponding one of the convex rail surfaces and a forward conductivesection spanning less than a gap distance between the convex railsurfaces, wherein the rear section and the forward section are adaptedso that when the projectile is accelerated along an energized pair ofparallel conducting rails, in a first stage of acceleration anelectrical current is produced across the rear conductive section as asolid armature to accelerate the projectile until the rear conductivesection is ablated prior to reaching the muzzle end of the barrel, andin a second stage of acceleration an electrical current is producedacross the forward section as a hybrid armature to accelerate theprojectile out through the muzzle end of the barrel.
 8. The railgunprojectile of claim 7, further comprising a non-conductive tail sectiontrailing behind the rear conductive section for precluding secondaryarcs.
 9. A railgun system comprising: a barrel having a breech end, amuzzle end, a pair of parallel conductive rails extending between thebreech and muzzle ends, with each conductive rail having a convex railsurface facing the other convex rail surface with only said convex railsurfaces of the rails adapted to contact (“rail-only contact”) aprojectile launched through the barrel; a barrel bore defined betweenand in part by said convex rail surfaces and having a cross-sectionalprofile (“non-conforming-to-projectile bore profile”) that does notcompletely conform to a cross-sectional profile of the projectile; andan enclosure surrounding the barrel bore and filled with a low-pressuregas, whereby the rail-only contact, the non-conforming-to-projectilebore profile, and the low-pressure gas in the enclosure contribute tominimizing plasma armature formation and restrikes; and a projectilehaving a nonconductive sabot, and a conductive section connected to thesabot and having a rear conductive section with a pair of contactsurfaces each for contacting a corresponding one of the convex railsurfaces, and a forward conductive section spanning less than a gapdistance between the convex rail surfaces, wherein the rear section andthe forward section are adapted so that upon connecting the conductiverails to a voltage source, in a first stage of acceleration anelectrical current is produced across the rear conductive section as asolid armature to accelerate the projectile until the rear conductivesection is ablated prior to reaching the muzzle end of the barrel, andin a second stage of acceleration an electrical current is producedacross the forward section as a hybrid armature to accelerate theprojectile out through the muzzle end of the barrel.
 10. The railgunsystem of claim 9, wherein the barrel further includes a pair ofdielectric sidewalls each having a dielectric sidewall surface facingthe other dielectric sidewall surface, with the dielectric sidewallsurfaces defining in part the barrel bore and positioned so as not tocontact the projectile.
 11. The railgun of claim 10, wherein thedielectric sidewall surfaces have an energy absorbing material thereoncapable of vaporizing to a low-temperature dielectric gas.
 12. Therailgun system of claim 9, wherein the pair of conductive rails aresegmented along the length of the barrel with each rail segment poweredindependently from other segments.
 13. The railgun system of claim 9,further comprising at least one additional pair of parallel conductiverails (“augmenting rails”) positioned adjacent the first pair ofparallel conductive rails.
 14. The railgun system of claim 9, furthercomprising an injector connected to pre-accelerate the projectile into abreech end of the barrel.